var plusOne = function(digits){
    let str = digits.join("")
    console.log(str)  //"123"
    console.log(typeof str) //字符串
    let num = parseInt(str)
    console.log(typeof num) //number 数字
    let num1 = num + 1
    console.log(num1) //124
    str = num1.toString().split("")
    console.log(str) //[ '1', '2', '4' ]
}

plusOne([1,2,3])
